Shrink tunnel



April 4, 1967 v F. G; SHANKLIN 3,312,811

SHRINK TUNNEL Filed Feb. 4. 1964 s Sheets-Sheet 1' u lllL'mlmllllllllun'INVENTOR.

BY FRANK GARRETT SHANKLIN a/ yew ATTORNEYS April 4, I967 F. G. SHANKLIN3,312,811

SHRINK TUNNEL Filed Feb. 4, 1964 6 Sheets-Sheet 2 FIG. 2

FRANK GARRETT SHANKLIN Forte! ///%en ATTORNEYS April 4, 1967 F. G.SHANKLIN SHR I NK TUNNEL 6 Sheets-Sheet 5 Filed Feb; 4, 1964 FIGS INVENTOR.

FRANK GARRETT SHANKLIN BY J an? EWW ATTORNEYS April 4, 1967 F. G.SHANKLIN SHRI NK TUNNEL 6 Sheets-$heet 4 Filed Feb. 4, 1964 I I N VENTOR. FRAN K GARRETT SHAN KLI N BY fowEw ATTORNEYS P 4, 1967 F. G.SHANKLIN 3,312,811

SHRINK TUNNEL Filed Feb. 4, 1964 6 SheetsSheet 5 ATTORNEYS p i 4, 1967 vF. G. SHANKLIN 3,312,811

I SHRINK TUNNEL Filed Feb. 4, 1964 6 Sheets-Sheet 6 INVENTOR.

FRANK GARRETT SHANKLIN BY ATTORNEYS United States Patent TUNNEL FrankGarrett Shanklin, Hemlock Park Drive,

' Groton, Mass. 01450 Filed Feb. 4, 1964, Ser.'No. 342,341 8 Claims.(Cl. 219-388) Thisinvention relates to a hot air shrink tunnel forshrinking packages formed from heat shrinkable plastic films aboutarticles contained therein. More especially it relates to a shrinktunnel adapted to direct to a flow of hot air at a relatively highvelocity directly against the surface of a package formed of heatshrinkable film'in such manner that the film shrinks uniformly withoutany local overheating,

The shrink packaging technique has become an important factor in theflexible packaging art in recent years. In this technique the article tobe packaged is placed in a loosely fitting bag or overwrap of a flexibleplastic material in film form capable when heated to an elevatedtemperature below its melting point of substantially reducing its area(i.e. shrinking). Thereupon the film is heated to its shrinkingtemperature and the loosely fitting bag or overwrap shrinks into a tightattractive conforming fit with the contents of the package. Unless forsome particular reason some special effect is desired the shrinkage ofthe film is carried out ideally under conditions wherein all portions ofthe film are heated uniformly to the shrinking temperature and whereinlittle, if any, heat is transferred to the contents.

When the shrink packaging art was first developed the film then incommon use had a shrink temperature below the boiling point of water.Under these circumstances shrinking could be conveniently carried merelyby dunking the package into a pot of boiling water, or by passing thepackage through a deluge of boiling water. Because of the high heatcapacity of water, and because of the excellent contact between thewater and the film, shrinking could be carried out under thesecircumstances substantially uniformly in a very short period of time,and if the package was removed from contact with the water soon enoughwith very little heating of the contents. On the other hand even withthese early films which had a low shrinking temperature the hot watertechnique could not be used unless the package was tightly sealed beforeshrinking, and unless the film was free of pin holes or other defects.Indeed in most instances it was necessary to evacuate the package beforesealing and before shrinking. With the passage of time new films weredeveloped having better physical characteristic than those originallyused. But these new films for the most part had a shrinking temperatureabove the boiling point of water. In a few instances where thistemperature was not too much in excess of the boiling point of watersolutions such as ethylene glycol solutions having an elevated boilingpoint where used in place of Water. The use of such solutions however,increased the cost of shrinking and increased the possibility ofcontaminating of the contents of the packages in the event of a leak inthe seal or a hole in the film.

To overcome these ditficulties and to permit the use of the shrinkpackaging technique with unsealed packages, hot air shrink tunnels weredeveloped. Such tunnels generally consists of little more than anenclosed box provided with a conveyor belt for carrying the wrappedarticles therethrough and with means usually one or more fans adapted toblow air over heated resistance wires (not unlike portable hair driers)for heating the air contained therein. In all of the conventional hotair shrink tunnels the velocity of the air in the region of the packagespassing therethrough is relatively low. When used with films that arerelatively easy to shrink, acceptable, though not ideal results, may beobtained in such tunnels using air 3,312,811" Patented Apr. 4, 1967heated to a moderate temperature. Frequently however, since the rate ofheat transfer from the air to the film is relatively low the productwithin the film takes heat out of the film faster than it can be putinto the film from theair, and as a result the product at least where itis in contact with the film heats excessively and the film shrinksunevenly With wrinkles being produced where the product touches thefilm.

The only way in a conventional low velocity oven to increase the rate ofheat transfer from the air to the film is to increase the airtemperature. While such a measure may improve the shrink where the filmcomes into contact with the product it creates serious difficultieswhere the film is out of contact with the product. In such areas thefilm tends to be overheated resulting in a degradation of physicalproperties, or even in the melting of the film. Thus a conventional lowvelocity hot air shrink tunnel is of limited usefulness with many films.If the air is hot enough to heat the film which is in contact with theprod net to the shrinking temperature the film out of contact with theproduct may be degraded or even destroyed. On the other hand, if thetemperature is-maintained at a moderate enough level not to excessivelydegrade or destroy the film out of contact with the product theshrinkage of the film where it is in contact with the product may beincomplete. In general the more narrow the range of temperature at whichthe film Will shrink without melting, the more serious this dilemmabecomes and this problem has become particularly serious withpolypropylene for example, which must be heated to 300 F. to obtain a40% shrink but which melts at 340 F. approximately.

In order to overcome the difiiculties inherent in the conventional priorart hot air shrink tunnels I have developed a hot air shrink tunnel thatincorporates several desirable features. In order to increase thequantity of heat available for transfer to the film a large volume ofair is directed against the surface of the package. This air isrecirculated in a closed system in order to conserve the heat contentthereof. In order to break up and blast away the dead laminar layer ofair which surrounds any solid object such as a package, and to allow theheated air to come into intimate contact with the film thus transferringits heat to the film very rapidly these large volumes of heated air areimpinged directly on the package in the form of jets or cascades havinga velocity of 1500 to 2000 and preferably 3000, or even more feet perminute.

I have found that with the use of large volumes of air directed againstthe package in the form of high velocity jets or cascades the film inthe package is uniformly heated to shrink temperature very rapidly evenwhen the temperature is maintained at a level which is little, if any,higher than the desired shrink temperature. The rapid heating means thatthe package can be passed through the shrink tunnel very rapidly and theshrink can be accomplished with very little warming of the productwithin the film. The uniform heating of the film to the shrinktemperature produces packages of outstanding attractiveness.

My improved shrink tunnel is adapted to direct the high velocity jets ofhot air directly against the top and both sides of the package; directlyagainst the top and the bottom of the package or both. In addition,since jets or cascades of high velocity air tend to diffuse and losetheir velocity rapidly as they pass through regions of relatively calmair, means are provided for adjusting the location of the source 'ofsuch and rapidly from the outside of the tunnel even while the tunnel isin full operation. Because of its compact and efficient design my newtunnel can be produced and sold competitively with conventional shrinktunnels.

These and other features of my new shrink tunnel can jets or cascadeseasily' be best understood by reference to the description which followstaken in connection with the drawings, in which:

FIG. 1 is an overall view in perspective elevation of the shrink tunnelof the present invention.

FIG. 2 is a front elevation in cross section on lines 2-2 of FIG. 4.

FIG. 3 is a side elevation in cross section along line 3--3 of FIG. 4.

FIG. 4 is a top view with the covering layer of insulation removed.

FIG. 5 is a front elevation in cross section along line 22 but showing amodification of the shrink'tunnel.

FIG. 6 is a side elevation in cross section along line 3-3 showing thesame modification as shown in FIG. 5.

The shrink tunnel of the present invention generally comprises an ovenindicated generally in FIG. 1 at 11 which is mounted on a base 12 and isprovided with a tunnel 13 for the passage of articles therethrough. Aconveyor belt 14 is provided to carry packaged articles through tunnel13. Conveyor belt 14 may either be a part of a packaging line or asshown a separate conveyor belt 14 mounted on pulleys 15 and 16 whichpulleys are mounted on braces 17 and 18 mounted on base 12 may beprovided. The return run of belt 14 passes beneath base 12. Base 12 ismounted at the desired height on some convenient support such as legstructure 19.

Oven 11 is provided internally with a blower 21 powered by blower motor22 which is mounted externally o-f oven 11 on the top thereof on blowersupport brace members 23. Conveyor belt 14 may be driven by conveyordrive unit 24 which preferably consists of motor 25 and reduction gear26 mounted on conveyor drive base member 27 supported on leg member 19.A junction box 28 containing the blower motor control, the drive motorcontrol, and the thermostatic control for the heaters may be mounted onthe side of oven 11. A thermometer 21 may be provided to give visualindication of the air temperature within oven 11.

Oven 11 is a totally enclosed box-like structure provided with a topwall 31, two end walls 32 and 33, two side walls 34 and 35 and a bottom36. Walls 31, 32, 33, 34 and 35 are provided with a layer of insulatingmaterial to prevent or at least to minimize heat transfer from withinthe oven to the outside, and the walls may conveniently be formed from asandwich comprising an inner and an outer sheet metal skin (indicatedgenerally at 37 and 38) with a layer of insulating material (indicatedat 39) therebetween. Oven 11 may be conveniently assembled using anexternal frame indicated generally at 41 formed of angle irons to whichthe walls are fastened as indicated generally by fasteners 42. Base 12is formed of assembled channel irons of substantial depth fastenedtogether in a suitable manner. Oven 11 is fastened to base 12 by meansof angles 43 which extend along the base of side walls 34 and 35.Entrance to tunnel 13 is provided by an opening 44 of convenient heightand width formed adjacent base 12 in each end wall 32 and 33 at a pointmidway between side walls 34 and 35. Openings 44 may be provided with aflexible curtain (not shown) if desired to close off the entrance and toreduce the loss of heated air from the interior of oven 11. Conveyor 14is arranged to pass through openings 44 in contact with bottom 36 ofoven 11 or a suitable slide member arranged thereon. In the versionshown in FIGS. 1, 2, 3 and 4 where the air flow is directed at thepackages entirely from the top and the sides belt 14 may be aconventional temperature resistant conveyor belt. In the modificationshown in FIGS. 5 and 6 where the air is directed onto the packages fromunderneath an apertured belt, such as a wire mesh belt, must be used.

The upper portion of oven 11 is divided into two chambers, air feed.chamber 45 and air return chamber 46, by means of a partitioning wall 47which extends vertically between side wall 34 and side wall 35 from topwall 31 to a point about level with the top of openings 44. The

bottom of air feed chamber 45 is defined by floor member 55 whichextends horizontally between side walls 34 and 35 and between end wall32 and vertical wall 47' at substantially the height of opening 44 oftunnel 13. Blower 21 which is located in the upper end of air returnchamber 46 is a conventional centrifugal blower with a rotor indicatedat 48, an air intake indicated at 49, and an air outlet indicated at 51.Outlet 51 fits closely into a matching aperture formed in vertical wall47 so that all of the air passing through blower 21 is forced into thetop of air feed chamber 45. Blower 21 is of such capacity that the totalvolume of air contained within oven 11 is circulated many times aminute. Typically blower 21 has a rate of capacity in cubic feet perminute 40, or even more times the volume of oven 11 in cubic feet. Theairflow is generally downward in air feed chamber 45 and upward in airreturn chamber 46.

Air feed chamber 45 is provided at a midpoint with a plurality of heaterelements53 so arranged that all of the air passing through chamber 45comes into close assoi ation with the heated surface associated withheater clef ments 53. Preferably heater elements 53 may be electr1= calfin-strip type resistance heaters arranged side by side horizontallybetween sidewall 24 and side wall 25. An arrangement of six 1500 wattheaters has proven to be satisfactory for a structure 2 wide, 2 high and2 /2 long. It will be noted that because of the substantially completerecirculation of the air within oven 11 once the air within oven 11 isbrought up to temperature relatively little additional heat is requiredto maintain the air at the higher temperature. As the result all of theair within oven 11 remains once it is brought to temperature atessentially the desired temperature. Heater elements 53 are connected tothe electrical input for the shrink tunnel through heat insulatedjunction box 54 located on the outside of side wall 35. Junction box 54may be included within junction box 28 or may be mounted separatelytherefrom. Conventional thermostatic controls (not shown) with thesensing element thereof located in the lower portion of air feed chamber45 are provided to control the electrical input into heater element 53.The electrical input to heater elements 53 may be soarranged that anumber of these heater elements are disconnected from the power sourceonce the air comes to temperature, and the remaining heaters may beoperated under modulated control to avoid excessive temperaturevariation.

On either side of belt 14 there is provided on the-underside of floormember 55 a side air box 57. Both side air boxes 57 are substantiallyidentical and each comprises a totally enclosed structure indicatedgenerally at 58 having an open top and a removable face plate 59. Faceplate 59 is attached to box 57 by means of bolts 61 associated withbrackets 62 mounted on the side walls of box 57. Each side air box 57 ismounted for laterally recip rocal travel toward or away from the centerline of belt 14 on rails 63 mounted on the underside of floor member 55.The top portion of the side walls of box 57 and of face plate 59 are alllocated in close association with the bottom of floor member 55 thusmaking fioor member 55 effectively the top ofbox 57. An aperture 64,65.i s pro- "vided in floor member 55 to permit the passage of airthrough floor member 55 into each side air box 57. Apertures 64 and 65are so positioned that all portions of each such aperture opens only tothe interior of the associated side air box 57 independent of thelateral position of that air box. A screw member 66 pivotally mounted onside Walls 34, 35 and provided with an'external crank 67 passes intoeach said box 57 through the rear wall thereof and cooperates with athreaded member 68 affixed thereto provided to adjust the lateralposition of each said box 57 independently. Thus the position of eachside air box 57 may be adjusted laterally and independently merely byrotating the appropriate crank 67 located outside of oven 11.

Face plate 59 is a plate of substantial thickness and is provided with aplurality of spaced apertures 69 each acting as a nozzle directing theflow of air passing therethrough. Apertures 69 may he directedhorizontally or may be directed at an angle for instance, downwardly asindicated. Since side air boxes 57 fit closely against the bottom offloor member 55 substantially all of the air passing from air feedchamber 45 through either aperture 64 or 65 must pass through apertures69 in face plate 59 of the appropriate box 57, and is directed againstthe appropriate side of packages passing along belt 14. In use boxes 57which are adapted to pass above belt 14, are adjusted to a positionWhere face plates 59 are in close proximity to the side of the packagespassing along belt 14. The adjustability afforded by crank 67 and screwmember 66 permits ready relocation of boxes 57 from outside oven 11 inorder to accommodate packages of varying width.

Air is directed onto the top of packages passing along belt 14 from faceplate 71 on the bottom of top air box 72. Top air box 72 is suspendedfrom top 31 of oven 11 by means of screw members 73 and '74 pivotallymounted at 75 and 76 to top 31 and passing through threaded members 77and 78 afi'ixed to the top of body 79 of top air box 72. Screw members73 and '74 are interconnected by drive means including sprockets 81, 82and chain 83 and are driven simultaneously by crank 84. The verticalposition of box 72 is adjusted by turning crank 84. Face plate '71 isfastened to body 70 of air box 72 by means of bolts 85 and brackets 86and similar to face plates 59 is provided with a plurality of airdirecting apertures 87.

One end of top air box 72 fits closely against vertical wall 47 and airis admitted into air box 72 through apertures 90 formed in wall 47 abovefloor member 55. In order to insure that the effective aperture willremain constantin area the end of air box 72 adjacent wall 47 isprovided with two vertical baflles 88 and 89. Baflle 88 extendsvertically from the top surface of box 72 adjacent wall 47 and baflie 89extends vertically from the bottom of box 72 adjacent wall 47. Baffie 89terminates short of the top of air box 72 forming aperture 91. Aperture91 registers with aperture 87 in every position of top air box 72.Bafile 88 prevents leakage of air from the top portion of aperture 910when top air box 72 is in a lowered position. As a result the effectiveaperture leading into air box 72 remains substantially constant nomatter what position air box 72 may be adjusted to. Face plate 71 of topair box 72 forms the top of tunnel 13 in air return chamber 46.

The sides of tunnel 13 in air return chamber 46 are formed by screens 92and 93 which extend upwardly from bottom 36 between wall 47 and end Wall33 immediately adjacent the sides of top air box 72. The air forced into tunnel 13 passes through either screen 92 or screen 93 and to returnair chamber 46 where it is drawn into the intake 49 of blower 21.Screens 92 and 93 are mounted for easy removal in vertical channels 94affixed tothe surface of wall 33 and channels 95 depending from wall 47.The function of screens 92 and 93 is to prevent the introduction offoreign material into the air stream.

The velocity of the air passing through air directing apertures 87 andface plate 71, or air directing apertures 69 of face plate 59 isdetermined primarily as a matter of simple design, the velocity in eachcase being the function of the volume of air passing through theparticular air box in a unit of time divided by the effective total areaof the apertures. Where the relative total area of the apertures issmall thus giving a relatively high air velocity a substantial backpressure develops in each of the air boxes and in air feed chamber 45tending to equalize the proportional flow through each of the air boxesand through each of the apertures in the face plate of each. Dampers maybe provided in association with jet these face plates should be adjustedto within 2 inches of the side or the top as the case may be of thepackages passing along belt 14. It has been found that to obtain 'themaximum distance of persistence of the jet the thickness of the faceplate in the region of the aperture must be equal to or greater than thediameter of the individual apertures.

The modification shown in FIGS. 5 and 6 varies in two respects from thatversion of the shrink tunnel of the present invention shown in FIGS. 1through 4. One such variation lies in the fact that the face plates ofthe air boxes or plenum chambers are provided iwth channeled slotsinstead of perforations. A second variation is that means are providedfor directing high velocity air against the bottom of the packagedarticles from beneath conveyor 14. It is obvious that the slotted faceplates may be substituted for the apertured face plates as shown inFIGS. 1 through 4 and that a shrink tunnel may be pro vided in which airis directed against the packaged article from the top, thesides and thebottom, as well as either the top and the sides or the top and thebottom.

In providing the shink tunnel with means for directing air onto thepackaged articles from beneath, an elongated aperture into which isinserted face plate 101 is provided in bottom 36 beneath belt 14. Abottom air box or plenum chamber 102 is provided fastened to theunderneath of bottom 36. Air is supplied to bottom air box 102 on eitherside of tunnel 13 by means of passages 103 which lead from apertures 104provided in floor member 55 of air feed chamber 45 through cooperatingapertures provided in bottom 36 to bottom air box 102. A damper 105 maybe provided in passage 103 to adjust the proportional air flow throughface plate 101 as compared to the air flow through face plate 71' of topair box 72. Since bottom air box 102 is located beneath the level ofbottom 36 it may extend as far along the path of belt 14 as may bedesired without alteration of the basic structure of the shrink tunnel.Face plate 101 throughout its length extends substantially the fullwidth of belt 14, which belt as mentioned above, is provided withsuitable apertures to permit a substantially unimpeded flow of highvelocity air therethrough.

In the slotted face plate structure as shown in face plate 71' and faceplate 101 in FIGS. 5 and 6, air passages are provided by mountingchannel elements 106 on a frame (not shown) with gaps or passages 107between adjoining channel elements. In the slotted face plate as in thecase of the face plate provided with apertures, a desirable welldirected blast of air is achieved when the height of the wall in the gapis equal to or greater than the width of the gap. Thus in a typicalslotted face plate the channel elements are approximately 3% incheswide; the gap between adjoining elements is approximately inch and theheight of the wall in the gap is approximately /2 inch. It has beenfound that such a face plate works almost equally effectively increating well directed high velocity blasts of air independent of thedirection of the air flow therethrough. In order to obtain uniformshrink however the gaps should be arranged transversely to the directionof travel of the packages through the tunnel so that all portions of thepackage pass through the same curtain of air. One particular advantageof the slotted face plate structure over the apertured face platestructure shown in FIGS. 1 through 4 lies in the fact that the highvelocity of the jets or cascades of air emitted through the slotspersists under operating conditions for approxi mately 4 inches ascompared to the two inch persistence of the jets created by theapertured face plates. This difference is presumably due to the reducedinterference between adjoining air streams in the slotted face plate ascompared to the apertured face plate.

It will be noted that the modifications to the basic shrink tunnel shownin FIGS. 1-4 to equip such a tunnel for a bottom air flow as shown inFIGS. 5 and 6 are relatively minor. For this reason the common elementsin both showings have been given the same reference number. Itwill befurther noted that passages 10 3 which feed air to bottom air box '102havebegen placed adjacent to side walls 34 and 35 to permit the additionof side air box structures similar to side air boxes 57 as shown inFIGS. 2 and 3. It is contemplated that in the event that both a bottomair box and side air boxes are provided separate apertures feeding suchair boxes would be provided in floor 55.

A particular advantage of the shrink tunnel shown lies in the fact thatsubstantially full recirculation of the air is achieved. This isaccomplished by the fact that the return air passage through the tunnel13 and return chamber 46 is completely free and unimpeded and that allportions of air feed chamber and the respective air feed. boxes wherethe air is under pressure are completely sealed from the outside. Thispermits very large volumes of air as compared to the volume of theshrink tunnel itself to be recirculated at a relatively low cost for theenergy required to heat the air. A large volume of recirculated aireffectively prevents the creation of any hot spots but rather permitsall of the air within the shrink tunnel to be maintained atsubstantially a uniform temperature. The use of apertured face plates torestrict the large volume flow of air causes an appreciable staticpressure to be built up behind the face plate. When the air escapesthrough an aperture in the face plate, it is driven at high velocity.Thus the large volume of recirculated air, together with the pressurebuild up behind the face plates, permits the establishment of highvelocity air jets or cascades which effectively scour the surface of thepackages as explained above. This scouring increases the rate of heattransfer very drastically and the large volume of air involved has asufiicient capacity to heat the film to the shrinking temperature veryrapidly (without cooling the air appreciably) thus achieving a veryrapid and uniform shrinkage of the film using air which is heated onlyto the desired shrink temperature. The relatively low temperature of theair as compared to the conventional shrink tunnel and the rapid passageof the package through the tunnel permitted by the high rate of shrinkpractically eliminates any possibility of the contents of the packagebeing heated or the wrapping film being damaged.

I claim:

1. In a shrink tunnel for shrinking heat shrinkable film into closecontact with the contents of a package formed at least in parttherefrom, said tunnel including a box-like structure having a passagepermitting transport of packages therethrough, means for transportingpackages in a predetermined path through said passage, circulating meansfor circulating the air contained therein, heating means for heating theair contained therein, said circulating means having a circulatingcapacity expressed in terms of volume of air circulated per minutesubstantially in excess of the cubic capacity of said structure, a firstduct means for directing the air from the circulating means to thevicinity of said passage, and a second duct means for directing the airfrom said passage to said circulated means, said first duct meansincluding a stationary enclosed air feed chamber and at least onemovable en closed air feed box, one side of said box arranged parallelto and contiguous to one side of said chamber, said air feed box havingan apertured baffie plate in one wall thereof, the wall of said boxincluding said baffie plate forming a wall of said passage, the adjacentcontiguous sides of said chamber and said box being provided with matingapertures for the passage of air therethrough, the

effective area of said apertures being substantially greater than thetotal area of the apertures in said baffle plate whereby air ismaintained under a substantial pressure within said chamber and said boxand is forced through the apertures in said bafile plate at a highVelocity, and baffle plate positioning means for adjusting the positionof said box toward and away from the predetermined path whereby theclearance between the baflle plate and the packages being treated may beadjusted and the air may be directed directly onto the surface of thepackages.

2. A shrink tunnel as claimed in claim 1 wherein the baffle platepositioning means are actuatable externally of said box-like structurewhereby the location of said baffle plate may be adjusted while saidtunnel is in use.

3. A shrink tunnel as claimed in claim 2 wherein the velocity of the airemitted from said apertured baffle plate is at least 1500' per minute.

4. A shrink tunnel as claimed in claim 2 wherein said apertured baffleplate has a substantial thickness and the apertures therein comprise aplurality of spaced holes passing therethrough.

5. A shrink tunnel as claimed in claim 2 wherein said apertured baflieplate comprises a plurality of spaced parallel channel members, thespace between adjoining said members forming a restricted channel forthe passage of air theret-hrough.

6. A. shrink tunnel as claimed in claim 2 wherein an adjustableapertured bafile plate is provided in the top and along at least oneside of said passage.

7. A shrink tunnel as claimed in claim 2 wherein an adjustable aperturedbafiie plate is provided in the top of said passage, a fixed aperturedbaffle plate is provided in the bottom of said passage, and said packagetransport means includes an apertured conveyor means.

8. A shrink tunnel as claimed in claim 2, wherein all the air passingfrom said first duct means to said second duct means passes through saidpassage, and wherein, in a portion of said passage, screen members areprovided, said screen members forming the entrance to said second ductmeans from said passage.

References Cited by the Examiner v UNITED STATES PATENTS 1,910,8685/1933 Webb 34-222 X 2,113,770 4/1938 Richardson 219-388 X 3,156,81211/1964 Forman et a1. 219388 X 3,160,153 12/1964 Drayer 219-391 X3,173,384 3/1965 Dersch et al 263-8 X 3,222,800 12/1965 Siegel et al.53-184 X ANTHONY BARTIS, Primary Examiner.

RICHARD M. WOOD, Examiner.

C. L. ALBRITTON, Assistant Examiner.

1. IN A SHRINK TUNNEL FOR SHRINKING HEAT SHRINKABLE FILM INTO CLOSECONTACT WITH THE CONTENTS OF A PACKAGE FORMED AT LEAST IN PARTTHEREFROM, SAID TUNNEL INCLUDING A BOX-LIKE STRUCTURE HAVING A PASSAGEPERMITTING TRANSPORT OF PACKAGES THERETHROUGH, MEANS FOR TRANSPORTINGPACKAGES IN A PREDETERMINED PATH THROUGH SAID PASSAGE, CIRCULATING MEANSFOR CIRCULATING THE AIR CONTAINED THEREIN, HEATING MEANS FOR HEATING THEAIR CONTAINED THEREIN, HEATING ING MEANS HAVING A CIRCULATING CAPACITYEXPRESSED IN TERMS OF VOLUME OF AIR CIRCULATED PER MINUTE SUBSTANTIALLYIN EXCESS OF THE CUBIC CAPACITY OF SAID STRUCTURE, A FIRST DUCT MEANSFOR DIRECTING THE AIR FROM THE CIRCULATING MEANS TO THE VICINITY OF SAIDPASSAGE, AND A SECOND DUCT MEANS FOR DIRECTING THE AIR FROM SAID PASSAGETO SAID CIRCULATED MEANS, SAID FIRST DUCT MEANS INCLUDING A STATIONARYENCLOSED AIR FEED CHAMBER AND AT LEAST ONE MOVABLE ENCLOSED AIR FEEDBOX, ONE SIDE OF SAID BOX ARRANGED PARALLEL TO AND CONTIGUOUS TO ONESIDE OF SAID CHAMBER, SAID AIR FEED BOX HAVING AN APERTURED BAFFLE PLATEIN ONE WALL THEREOF, THE WALL OF SAID BOX INCLUDING SAID BAFFLE PLATEFORMING A WALL OF SAID PASSAGE, THE ADJACENT CONTIGUOUS SIDES OF SAIDCHAMBER AND SAID BOX BEING PROVIDED WITH MATING APERTURES FOR THEPASSAGE OF AIR THERETHROUGH, THE EFFECTIVE AREA OF SAID APERTURES BEINGSUBSTANTIALLY GREATER THAN THE TOTAL AREA OF THE APERATURES IN SAIDBAFFLE PLATE WHEREBY AIR IS MAINTAINED UNDER A SUBSTANTIAL PRESSUREWITHIN SAID CHAMBER AND SAID BOX AND IS FORCED THROUGH THE APERTURE INSAID BAFFLE PLATE AT A HIGH VELOCITY, AND BAFFLE PLATE POSITIONING MEANSFOR ADJUSTING THE POSITION OF SAID BOX TOWARD AND AWAY FROM THEPREDETERMINED PATH WHEREBY THE CLEARANCE BETWEEN THE BAFFLE PLATE ANDTHE PACKAGES BEING TREATED MAY BE ADJUSTED AND THE AIR MAY BE DIRECTEDDIRECTLY ONTO THE SURFACE OF THE PACKAGES.